CO2 vs Nitrogen for chilling vessels


#1

What do you prefer for chilling and why? I use CO2 and it does a great job, but I don’t know much about using liquid nitrogen for the same applications.


Freezing Material column w/ LN2
Dewar Ditty
#2

:beers: :popcorn:

LiqCO2 or dry ice?


#3

Personally Ive never used nitrogen, however LCO2 gets the job done from my experience.


#4

What are you cooling? Hydrocarbon extraction? Ethanol?

Are you keeping it pressurized? How do you avoid dry ice build up?
I’ve seen talk of PRV’s freezing up and causing problems…

My Airgas guy wants me to use CO2 for cooling ethanol so I don’t freeze it, which seems like a valid concern.

He agrees that we can probably make direct LiqN2 injection work.

I could also direct inject LiqCO2, but then I’m getting into a different solvent system, and would need to retool.


#5

say what? Are you wanting to put ethanol in liquid Nitrogen? Or just using a cooling coil? Liquid CO2 is nice and cold for tumblers, N2 is colder than I have seen needed for any process on this site.

At least in situ. Can provide a better answer with some idea of what you want yo use it for.


#6

Liquid


#7

Using it for heat transfer in a hydrocarbon system


#8

It’s a hydrocarbon system. I use it for heat exchange and chilling tanks. Yea I keep it pressurized and I’m constantly monitoring it for dry ice buildup.


#9

liquid CO2 correction: I spaced the whole sublimation thing. No coffee yet.

If your packing dry ice and ethanol thats fine. A pressurized liquid N2 system would be pretty badass if you could control the amount of contact to mediate the extreme temps.

A final safety note, can’t help it, CO2 use requires ventilation. N2 use does as well, but not nearly as much. Much less likely to die from asphyxiation with N2.


#10

I may very soon try injecting LN2 into a jacket partially filled with coolant (i.e. ethanol). As long as the temperature is monitored, there shouldn’t be any reason it gets too cold.

I’ve been meaning to do some math on that note exactly (for cooling ethanol in a vessel). I originally calculated how much boiling nitrogen would remove the necessary heat, but I didn’t account for cooling a volume of ethanol that would then cool another larger volume of ethanol. The volume of the cooling bath will surely play a role, but I’ll see how heavily it affects the math (volume may be specific to the vessel/jacket capacity)

It has been brought up to me many times how real the Leidenfrost effect is with nitrogen. That’s why the cooling bath might be necessary (unless you want to use crazy amounts of nitrogen). However, I believe Gray Wolf used to tell me he installed some direct-injection jacketed coils using liquid nitrogen and it worked great. I believe Bizzybee also brought a column down well below -100C but I imagine that required lots of nitrogen.


#11

Does the dry ice formation happen upon venting CO2 too rapidly? What is the emergency protocol if dry ice clogs the vent line?


#12

object of the game is to cool the Ethanol to approximately dry ice temps. or an arbitrary temp below ambient. on demand. repeatably.

Airgas guy did suggest LiqAir as a non-suffocating option. Claimed NASA doesn’t worry about the O2 separating out, so we should be fine…but the idea of liqO2 in my EtOH just doesn’t work for me.


#13

I’d argue that your body will scream at you as the CO2 gets too high.
It won’t make near as much fuss when the N2 takes you below 19% O2.
I’d have to admit that I haven’t gotten close with N2. I have however experienced & witnessed dangerous CO2 levels. I agree you won’t always get enough warning

I once rescued a couple of teens from a pool that had had 50lb of dry ice thrown into it at a party. I noticed their distress just in the nick of time.

I agree that you can vent more N2 into the room than CO2 and still make it out alive.


#14

To me that sounds like adding an oxidizer! Probably bump up the flamibility 10 fold!


#15

true, but you have heard of nitrogen narcosis? Could be fun for a bit…

you will notice loss of oxygen from anything eventually. A couple more pieces of the puzzle:

N2 = Lighter than air = rises = 78.09% of the atmosphere

CO2 = heavier than air = sinks = 0.04029% of the atmosphere

Proportionally those are off gassing events are orders of magnitude less effecting the makeup of your air.

It’s just my instinct to qualify anything I say that could be dangerous. Lots of people here know things, others don’t.

I have 40 ft ceilings and no ventilation, so for me N2 is a better choice. It’s been an ongoing argument with my partners. I want some ventilation!


#16

Once upon a time “safe” meant that if I kept the air stirred, I could vent my entire butane store and be 2 orders of magnitude below the explosive limit.

I’ve got way better tooling now, just wish someone had talked to the city before starting construction. Pissing off the permitting troll has cost us dearly.

Edit: didn’t get my diving cert, but did take the training once upon a time. Wasn’t aware N2 Narcosis could be induced at atmospheric pressure without first inducing O2 deprivation. Zero data.


#17

Safety 1st is almost always a great policy…

You do know the meaning of “safety meeting” right? :wink:


#18

what I did and do as a free citizen is one thing. What I say to other people is another. And what I do in a licensed lab is yet another ridiculously controlling, straight on OCD, laser focused like sharks with lasers on their heads on not only being safe but being 100% legal.

Blowing myself up, inhaling toxic fumes, getting hot solvent on my arms or otherwise damaging myself and my immediate surroundings is for fun time :crazy_face:

and a safety meeting according to bylaw 103 subsection ICXVIII paragraph 4 clearly states that all safety meetings be held in a suitable location such as Mt. Hood Meadows, or in back of Science Building 3.


#19

Back on topic. Or at least close. You can get serious burns at these temperatures. even at -40C if you try. cold stainless can stick to skin. wear appropriate personal protective gear. even if it doesn’t stick, less than a second in contact with stainless at -80 will leave a burn. the Leidenfrost effect that protects you from the full effect of dry ice and LiqN2 doesn’t help you here (being below the b.p of SS :wink: ). Same goes for the cold ethanol. no built in insulating safety blanket. because you’re again well below the boiling point.


#20

co2 takes time to dissolve into solution so bubble thru might not change ur solvent that much